Preparation of degraded allyl starch



Patented Oct. 28, 1952 ARCH Kenneth C.' Hobbs,Berwyn, Ill., assignor to Corn Products" Rfining Company-New York; NL-Y., a corporationpf'New J ersey No'DrawingL Application January 19,1948, 4 Serial No. 3,170

This "invention relates; generally; to the -preparation of allyl starch; and more particularly, allyl starch which is soluble an organic solvents".

The primary reaction involved ir'rrthe preparation' of' allyl" starch =is -considered n) be one between an' alkali starch comple'x and-"anallyl halide: In carrying out this reaction; the" alkali starch complex maybe either "pro-prepared and used" as such or prepared insitu "from-starch and alkali in proper concentration and"quantity to yield the complex: Prior to -this invention; it was considered necessar-y to carryout this primary reaction in the-presence ofanon-re actant, organic solventpsuchas toluene, acetone, dioxane or isopropyl alcohol;

When" the allylhalide-usedi in the primary reaction is allyl' chloride; it" previously has been inconvenient w obtain an al'ly-l 1 starch product" WhiCh'iS soli'ible'in' organic sol'ventsr One important object'of this invention is the provision" of a method of "preparing allyl starch" by reaction between anf allyl halide and 1 an alkali starch complex-' (either' 'pre prepared or prepared in situ), wherein an 'excess =o'fallyl halide-over that required in the reaction is used as the reaction medium.

Another important object of'the invention'is the provision of a'method 'of preparing allyl starch, using "allyl' chloride-as the reactive allyl halide, wherein' theallyl' starch initially formed O isfirst :de'g'radedto soluble formand then-puriwithoutprecipitation-of the allyl starch;

Certainzother:objects; of .Tthe invention 1. will;

hereinafter...

For: az-more complete. understanding of 5: the natureand scope of the inventiomreference may: be hadytothe -=foll0wing detailed description thereof wherein :a-number of presently vpreferred embodiments of the invention are given-byway of illustration in the specific examples.

It has been found that under certain cone. ditions; starch reacts with alkali metal hydroxide to form an alkali starch 'complex'which undergoes the typical reactions of'an alkoxide. This alkali starch complex may be prepared by mixing starch" with =at least' a suflicient amount of a suitable organic liquid such as isopropyl alcohol or allylhalide-t0-wet--the-starch,and then reacting such wetted starch, preferably under con+ ditions of agitation, with an' aqueous alkali h'ydroxideiat a concentration of at least 35 per cent. It may also be prepared in situ by merely mixing" together starch; alkali metal" hydroxide IOFClaimstr (01. 2604333) and aliyl" halide: It was- -further-* "found that insofar as the" primaryreaction: resulting in" allyl starch is concerned, the content of alkali in*the alkali starch complex determines the con sumption" of" the 'allyl halidein' the reactionq Thus, if the alkali starch complexi contains only 2' moles of'alkali per" glucose residuathem no more "than 2 moles of'allylhalide can: baconsumed in' 'the primary reaction resulting in allyl starch; Accordingly when-an excess of 'allyl halide-is'used as-the reactidnmediiam in accordance with. this invention; this" excess can be readilyrecovered! 'Ifhis' expedient has been found to provide" several important aclva ntages; In the first place,

itiis obviously an advantage in this type of "re-'- action" to utiliz'e -an""e-xcess*of one of""the:rre= actants as 'the reaction medium; rather than a non-reactive organic-solvent; A much more significant" advantage "is the marked increase in" However; when allyl chloride "is used; the "ally'lstarch initially formed 'is"relatively insolulzvlekin organic solvents; Th'erefore, a- I second stage in the 'process isrequirecl wherein the initial: insoluble product is solubilized; presumably through degradation since there "is' 'little for no increase in the degree of etherificationtinxthis second.

allylstarch greatly shortened by employing the acidified water-immiscible alcohol, but also it has been found that the solubilized allyl starch may be readily purified by aqueous extractions without causing the allyl starch to be precipitated as a gum. From a practical operating standpoint, this is a very important advantage since it avoids the inconvenient kneading of a gummy mass with water which has been previously required.

The following example will illustrate the presently preferred embodiment of the invention:

EXAMPLE 1 Eight hundred parts of corn starch are slurried in 2200 parts of allyl chloride in an autoclave. The slurry is cooled to C. or below, and 710 parts of 50 percent sodium hydroxide are added with good agitation. The autoclave is sealed and the contents heated to 95 to 100 C. After holding at this temperature for one hour, the autoclave is opened and the contents are diluted with 4400 parts of n-butyl alcohol. The pH of the mixture is adjusted to 1.0 by the addition of hydrochloric and the excess allyl chloride (1475 to 1500 parts) is recovered by distillation. The temperature of the allyl starch solution is raised to 90 to 100 C. during the final stages of the distillation and is held within this range for minutes in-order to degrade the allyl starch to a soluble stage. The mixture is then cooled and extracted with water until neutral and free of salt and other watersolubles. The final step consists of concentratin the n-butyl alcohol solution of solubilized allyl starch to the desired concentration. The allyl starch product contains from 1.5 to 1.7 allyl groups per glucose residue and is readily soluble in organic solvents, such as dioxane, toluene, etc. The concentrated allyl starch solution is adapted to be conveniently handled and stored, and is in a condition ready for use.

The foregoing process may be modified in a number of respects. Insofar as the excess of allyl chloride over that consumed in the primary reaction is concerned, it is preferred to use enough so that the reaction mixture will be fluid and easy to handle. There appears to be no advantage in using more than this, while smaller amounts result in the mixture becoming increasingly more viscous and difficult to handle.

In the above example, the amount of sodium hydroxide used '(i. e. 355 parts, dry basis) is equivalent to 2 moles per glucose residue. However, the ratio of alkali to starch may be as low as 1.5 and as high as 4.0. The optimum concentration of the aqueous alkali solution is within the range of to percent. Lower concentrations result in increasing losses of the allyl halide through hydrolysis. On the other hand increased concentrations tend to decrease the rate of reaction and, also, decrease the fluidity of the reaction mixture. Potassium hydroxide may be used, but it is more expensive and appears to offer no advantage.

With respect to the temperature at which the primary reaction is carried out, this should be within the range of to 100 C., with to C. being the preferred range. Because these temperatures are well above the boiling point of allyl chloride, the reaction must be carried out under pressure in a closed Vessel. The reaction is exothermicand no additional heat is required after'the reaction has been initiated.

At any given temperature, the reaction time depends primarily on theconcentration of the alkali. It should be lon enough so that after completion, the reaction mixture is at least nearly neutral. When a 40 per cent concentration of alkali is used, the time at 100 C. may be reduced to about 30 minutes.

Enough n-butyl alcohol is used to dissolve the allyl starch formed. However, the exact amount is not critical. Instead of n-butyl alcohol, a mixture of amyl alcohols or other water-immiscible alcohols may be used. Solutions of allyl starch in these solvents may be extracted with water without causing the allyl starch to precipitate.

Alcohols are preferred for this purpose because the conditions for the rupture of the glycosidic linkages are morefavorable with an alcohol than with an inert solvent.

The concentration of the hydrochloric acid in the n-butyl alcohol may be varied considerably depending upon the degradation time and temperature used and the degree of degradation desired. A concentration within the range of 1.0 percent to 2.5 percent based on the weight of the original starch may be used. If desired, an equivalent amount of strong sulfuric acid may be used instead of hydrochloric acid.

The temperature at which the degradation is carried out may be varied considerably depending. upon the concentration of strong acid in the water-immiscible alcohol, and the time of degradation. The latter factor may vary between 15 minutes to 90 minutes.

The following examples will serve further to illustrate the invention: a

EXAMPLE 2 To a moist mixture of 18 g. of corn starch and 5 ml. of 91 per cent isopropyl alcohol was added 32 g. of a 50 percent sodium hydroxide solution. After a few minutes of vigorous stirring, an exothermic reaction occurred and the mixture progressively changed from a smooth slurry to a semi-dry powder. This pre-prepared alkali starch complex was transferred to a 500 m1. three-necked round bottom flask and ml. (g) of allyl bromide was added. The total Weight of this mixture was 240 g. The mixture was rapidly heated to reflux temperature (66 C.) and samples were removed during the course of the reaction. These samples were titrated to phenolphthalein end point with 0.0987 N hydrochloric acid in order to determine the rate of alkali consumption, which in the early stages is considered tobe nearly identical with the rate of etherification. It has been demonstrated that allyl halides are hydrolyzed very slowly in concentrated alkali solutions. The following table shows that suflicient alkali was consumed during the first 2 minutes to give a product having two allyl groups per glucose residue, for 4 moles of alkali per glucose residue was originally present: 7

TABLE 1 Rate of reaction between alkali starch complex and allyl bromide at 66 C.

Moles of I Percent of NaOH Coll- Time, Mmutes NaOH Consumed Per sumed Glucose Residue After a total of 70 minutes, the reaction was EXAMPLE The proceduregive'n' in Example 3ffwasrepeat} edtliree times; ,exceptf tha't ;onereactibn-.;wast dise continued; aiter one; hour, a the"; s'ecohd'fl. after 2 hours and: the; third after; 3 ho'urs; at irefiuxztem per'ature';. No improvementin.sOIubiIityQorin the. degree;- ofsubsti'tuti'o'n .wa's' observed'withf longer: reaction utim'es.

To: a l-suspension? of?) 18: g: .ofilcom'rsta'rch- :infi200' ml; .of 'failyli'chloride was added" a xsolutionicon tainingilZi gzzof: sodium? hydroxide'fin-"101ml; of water; 'Ihe suspensiorrwas warmedron the steam bath? until arreacti'on occurredfhetweenithe starch and the alkali. The mixture was then "trans fefrredstoxa oneeipint pressure bottleand the bottle sealed. The bOtflTWSZSZZ placed ".in a steam Bathi7aE 100 CI After' 'l'lihour's, .aclear ?yellow sohi'tiozrtoffallyl starchiinzthe excess allylrchloride" and raflayerixot moist. sodium-chloride were pres entir. The: mixture wasi-purified h simply de= canting the? allyl chloride solution" which was then: dilutediwithi 100 l ml. i of toluene; a'n'd the" excessallyl 'chloridewas recovered hydistillation; This; letteicleari solutioniof allylstarch' in toluenewhich was ready for use. The p'roduct was foiind to' fcontain lflii f allyl groups' per 'g1ueose residue. Thiszexperiment demonstrated the-lengthiof time" which: is required to degrade: ally} starc -to a soluhlastagezby heating iri allyl 'chldridet A mixture?containingiliiegr of' corn starch- 200 mli i of allylzchlorideyfl g;-fof sodium hydroxide and '7'- inh ofliwvaterxwaszitreated in thefsame manner dSCIibEdJiIf Example 5S. Inthis;iexperimerit only. twbzmoleszoi: fal'kali were added 'in'stead' of three; Theaprodiictiobt'ained wa'sfciund :to' contain lB allylgroups pen glucose residue.

EXAMPLE 7 EXAMPLE 8 A solution of 120 g. of sodium hydroxide in 100 ml: of water was added at room temperature to a slurry of 180 g. of corn starch in 200 ml. of allyl chloride. Gentle heating caused the alkali which thewis'cos'ity varied from 'fiio 'to oi e: starchicomplex ito fo'rm'iwith the evolutlonsorifa i considerable amount? of heat- A'nearly drytalkalii starch complex" resulted which weighed 400g; Fortyeg. of thisematerial was reacted with 60 ml. of;allyl'chloride*-at';'100'C. for one-hour. Itwas found' that 1.6 moles ofalkali per glucose residue had been-consumed.

A second $01K. of thealkalistarch complex was; reacted with 60 ml. of'fallyl chloride at 100 CI for: 2 hours-5 This product was found to contain:

lfl allylgroupstper gly'cose. residue, butit. was not completely;- soluble ;-in-. organic rsolventsiq This product :w-as a'dded :to 5100' ml; of n-butylalcohol which contained one ml. of concentrated hydro-- chloric acidi" The mixture was-heated on' 'the EXAMPLETQ i A solution-containing850 giof "so'diiim hydrox=-' idei in 9i'8 mll of wat'er was added to a' m-ixtu're of corn starch an'd lo' mli of allylchlorider A-d y alkali st'ar cli'complex'formedtowhich was: added-'80 mliof 'allyl cliloride: This mix-ture' was a heated for 2 hours at 95 C-.- A' soft"whitemass' of allyl starch coveredwith excess allyl chloride V resulted This'was dilutd witfi mfl'mllof n-butyl alcohol containing o'iie ml. of canceritrated hyu'te'sz- A clear fluid solution-resulted 'which' was" extfaet'ed witli three ml? portions of 'water irra- Six preparations of allyl starch wereacarrie'd out in: the *sam'e'=nianner"assthat described-51h Examp1e '-9;.:exc'ept' that" thei'reactioni'time 2betweeni" allyl chloride and alkali starch was only one? hour? Theixsamplestwereidegraded"in acidified n-tbutylai alcohol: fo'ri'va'rying lengths of tiin t: 1005 and purified to gii7e a-seriesi'of SKI-pert: solutions pf allyl starch in n-buty-l alcohol chlorid--was-- addedf Seven identical fmixtiiresl were prepared? The "reactibns- -were carried out a-t1'- l00 '"C?- and one was discontinued after minutes, two after minutes, two after minutes, and two after minutes. Each reaction mixture was immediately cooled, and the total alkalinity in one sample from each set was determined by titrating an aqueous suspension of the product to phenolphthalein end point with one N hydrochloric acid. The duplicate sample of each set was degraded in acidified n-butyl a1- acrasss Moles of NaOH Consumed Per Glucose Residue Allyl Groups Per Glucose Residue Reaction Time, Minutes This shows that the etherification reaction is essentially complete-in a little more than 15 minutes.

' When allyl bromide is used as the reactant allyl halide, the allyl starch formed appears to be soluble in organic solvents, and a degradation step is not required to produce a soluble product as in the processes wherein allyl chloride is utilized. However, degradation may be necessary to give an allyl starch having the desired viscosity. Because of its higher boiling point, the reactions using allyl bromide need not be carried out under pressure.

What is claimed as new is:

1. In the process of preparing allyl starch soluble in organic solvents, the improvement which comprises reacting alkali starch complex with allyl chloride to form allyl starch, and degrading the allyl starch in the presence of an acidified'water-immiscible alcoholic solvent for the degraded allyl starch.

2. The process of preparing allyl starch which comprises reacting alkali starch complex with allyl chloride in the presence of at least a sufficient excess of allyl chloride to prevent the reaction mass from solidifying and in the absence of any other organic solvent, adding acidified water-immiscible alcohol to the reaction mixture, heating the mixture to distill ofi excess allyl chloride and degrade the allyl starch to a soluble stage,- and washing with water the resulting solution ofsoluble allyl starch insaid water-immiscible alcohol to remove water-soluble impurities therefrom.

3. The process of claim 2 wherein the waterimmiscible solvent is n-butyl alcohol.

- 4. The process of claim 2 wherein the waterimmiscible solvent is acidified with hydrochloric acid.

5. The process of preparing allyl starch which comprises admixing starch with suflicient aqueous sodium hydroxide of 40 percent to 60percentstrength to provide 1.5 to 4.0 moles of sodium hydroxide, dry basis, to each glucose residue and with an excess of allyl chloride at least sufficient to prevent the reaction mass fromride and to degrade the allyl starch, and extracting the resulting solution of allyl starch in nbutyl alcohol with water to remove water-soluble impurities therefrom.

6. The process of claim 5 wherein the last amounts of said excess allyl chloride are distilled oil at a temperature within the range of to 100 C. and the reaction mass is held at such temperature for at least 30 minutes.

7. The process of preparing allyl starch which comprises slurrying 800 parts of starch with approximately 2200 parts of allyl chloride, adding to said slurry while maintained at a temperature not in excess of 25 0. approximately 710 parts of a 50 percent aqueous sodium hydroxide solution, heating the reaction mass in a closed vessel to a temperature within the range of to C. for approximately one hour, diluting the reaction mass with approximately 4400 parts of n-butyl alcohol, adjusting the pH of "the mixture to 1.0 by the addition of hydrochloric acid, recovering the excess allyl chloride from the reaction mass by distillation, the final stages of which are carried out at a temperature within the range of 90 to 100 C. with the reaction mass beingmaintained at such temperature for approximately 30 minutes, cooling the reaction mass, extracting the cooled reaction mass with water until neutral and free of salt, and concentrating the resulting solution of allyl starch in n-butyl alcohol.

8. A process of preparing organic solvent soluble allyl starch comprising allylating starch by heating it with allyl chloride in the presence of concentrated aqueous alkali metal hydroxide solution and in the absence of an organic solvent thereby forming organic solvent insoluble allyl starch, and after substantial completion of the allylation addingacidified n-butyl alcohol to the resulting reaction mixture and continuing the heating inthe n-butyl alcohol to render the allyl starch soluble therein.

9. A process of preparing organic solvent soluble allyl starch comprising allylating starch by heating it-with allyl chloride in the presence of concentrated aqueous alkali metal hydroxide solution and in the absence of an organic solvent thereby forming organic solvent insoluble allyl starch, and after substantial completion of the allylation adding acidified water-immiscible a1- cohol to the resulting reaction mixture and continuing the heating in said water-immiscible alcohol to render the allyl starch soluble therein.

10. The process of claim 9 wherein the waterimriiscible solvent is acidified with hydrochloric aci KENNETH C. HOBBS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS N umber 

1. IN THE PROCESS OF PREPARING ALLYL STARCH SOLUBLE IN ORGANIC SOLVENTS, THE IMPROVEMENT WHICH COMPRISES REACTING ALKALI STARCH COMPLEX WITH ALLYL CHLORIDE TO FORM ALLYL STARCH, AND DEGRADING THE ALLY STARCH IN THE PRESENCE OF AN ACIDIFIED WATER-IMMISCIBLE ALCOHOLIC SOLVENT FOR THE DEGRADED ALLYL STARCH. 